1. Field of the Invention
The invention relates to a shaft arrangement for relaying torques acting around a rotational axis, with a variably adjustable torsional stiffness acting around the rotational axis. Further, the invention relates to a method for relaying torques acting around a rotational axis with a variably adjustable torsional stiffness acting around a rotational axis.
2. Description of the Prior Art
Rotating systems for transferring rotational movements and torques, for example in the form of mechanical shafts, are subject to operationally induced torsional loads, which can lead to the formation of disruptive rotational oscillations, in particular given a discontinuous introduction of torque along the shaft. In particular shafts with a long and slender design, which only have a low torsional stiffness for systemic and structural reasons, tend to form such rotational or torsional oscillations, which additionally have resonant natural oscillations at already low frequencies, and hence can permanently detract from the operational comfort and operational acoustics. In all instances, these oscillations at the very least detract from the operational stability and associated system loadability of the respective shaft.
Typical examples of rotation transferring systems that are sensitive to rotational oscillations include drive trains in motor vehicles, especially since power output in internal combustion engines does not take place continuously through the individual cylinders, as a result of which the power output of the engine as a whole is accompanied by torque fluctuations, which have an especially detrimental impact in particular in cases where the frequency of these fluctuations lies within or is proximate to the natural frequencies for the ensuing rotationally movable systems in the drive train, for example the power train, transmission, steering system, etc. In these instances, the discontinuities caused by the internal combustion engine can lead to elevated oscillation loads, wear and noise generation, which noticeably detract from driving comfort.
In order to counteract such rotational oscillations, it obviously makes sense to elevate the torsion resistance of rotationally movable components with structural measures, most often by using stable shafts with as massive a design as possible, although this results in an undesired increased weight for the overall system, which would not appear to be beneficial in terms of cost and energy savings. Rather, it is imperative to find solutions that reflect the principles of lightweight construction, and also help effectively prevent oscillations from arising along rotating shafts of the kind described above.
One known possibility involves the use of oscillation damping components along a shaft arrangement that transfers the rotational movement. German Patent DE 100 02 259 A1 discloses a torque transferring device, in particular for the drive train of a motor vehicle, having a disk-shaped, axially elastic component whose axial elasticity is generated by providing suitably arranged transected areas in the form of a local component perforation. The disadvantage is that the transected areas yield a torsional stiffness characterizing the component that is irreversible and fixed. As a consequence, while rotational oscillations can be dampened within a fixed frequency range, work, ageing or system-related, frequency-specific changes take place in the arising natural frequencies of the rotational oscillations, causing the known torque transferring device to reach its technical limits.
By contrast, the shaft described in EP 2 278 183 A1 permits a variable adjustability of its torsional stiffness. To this end, at least one shaft section along the shaft referred to as a so-called torsion rod is provided with a shaft cross section that is reduced in relation to the remaining shaft region, and has a lower torsional stiffness than the remaining shaft region. Also provided is a tubular shifting collar that can be moved along the shaft, and is designed and situated in such a way as to bridge the area of the torsion rod, thereby directly joining the adjacent shaft sections together. In this way, the torsional stiffness of the shaft can be adjusted at least between two discrete stiffness values by moving the tubular shifting collar.
Even though it is possible to expand on the approach described above of gradually changing the torsional stiffness and increase the number of discretely adjustable torsional stiffness levels by providing several previously referenced torsion rods with respectively different torsion rod diameters along the shaft, the goal is still to have as smooth, that is, continuous variability for the torsional stiffness of a shaft arrangement acting around a rotational axis.
In particular with respect to the use of reduced-weight materials, for example light metals, fiber-reinforced composites, etc., the goal is to find solutions that are able to effectively suppress the formation of rotation-induced, disruptive oscillatory phenomena along rotating shaft arrangements.